Hydrodynamic conditions are one key parameter acting on biofilms. It is commonly assumed that hydrodynamic conditions shape biofilm morphology by inducing sloughing events, erosion or compression (Van Loosdrecht et al. 2002). Biofilm community structure can also directly or indirectly be influenced by hydrodynamics conditions (Rochex et al. 2008). But it remains unclear if a change in hydrodynamic conditions affects mature biofilm morphology and/or community structure. In the literature, biofilms are mainly studied either under constant shear, e.g. comparing two reactors where biofilms developed at two different shear rates, or as erosion tests as in Paul et al (2012) . In our study, we exposed biofilms to variable hydrodynamic conditions where the applied shear changed over time. Once matured, we exchanged biofilms with different shear histories and exposed them to a change in the hydrodynamic conditions. By this way, it is possible to study the adaptation of physical and microbiological structures of biofilms after a switch in the hydrodynamic conditions.